Circ. Pump Location; Home heating boiler


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Old 09-23-08, 06:29 PM
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Circ. Pump Location; Home heating boiler

I removed my 38 year old functioning forced hot water boiler on principle due to it's age and the impending Winter. Over the years I changed the Taco pump due to failure at least three times. I have a photo of the entire system I took before disassembly. The Pump was located on the OUTLET of the boiler.
I have installed my new boiler and put the pump in the same place, the outlet. I have purged the air, fired it up, and done a shakedown cruise and it works flawlessly.
I now have taken a closer look at the diagrams included in the new boiler's literature and it clearly shows the pump on the boiler INLET! Nowhere on Taco's website, or any other search I have done does it say where to put the pump. Now I'm confused and have shut down the boiler until this is resolved. Can anyone advise me: Inlet or Outlet?
BTW, it's a HydroTherm HW125 Gas fired, 125K btu input unit.
 
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Old 09-23-08, 07:03 PM
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For "standard" boilers like the Hydrotherm, the important relationship between the heat source (boiler), the expansion tank (ET), and the circulator (pump) is the order in which they occur.

If the pump is on the outlet (supply) side, then the order, in the direction of water flow, should be: boiler, ET, pump.

If the pump is on the inlet (return) side, then the order, in the direction of water flow, should be: ET, pump, boiler.

This is called "pumping away" and has a lot of threads here with info.

In practice, it often doesn't matter. If the system is working acceptably, chances are everything is fine.

You could post some photos of the system, host them at photobucket.com and provide links here.
 
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Old 09-23-08, 07:56 PM
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Originally Posted by xiphias View Post
For "standard" boilers like the Hydrotherm, the important relationship between the heat source (boiler), the expansion tank (ET), and the circulator (pump) is the order in which they occur.

If the pump is on the outlet (supply) side, then the order, in the direction of water flow, should be: boiler, ET, pump.

If the pump is on the inlet (return) side, then the order, in the direction of water flow, should be: ET, pump, boiler.

This is called "pumping away" and has a lot of threads here with info.

In practice, it often doesn't matter. If the system is working acceptably, chances are everything is fine.

You could post some photos of the system, host them at photobucket.com and provide links here.
Thanks Xiphias, I searched 'circulator location' and did indeed come up with some useful info. It looks like either position is OK but generally the outlet side (pushing away) is the best way in regard to reducing cavitation and maintaining even pressure.
Unfortunately I have a little repair to make. I installed in this order; outlet, circulator, ET (located under the air separator). I will make it outlet, ET, circulator.
One more question though. Should I run the fresh water makeup line (regulated to 12-15psi) into the air separator?Right now it is in the return line, four feet from the inlet, where it has always been. One of the articles you referred me to said that this can result in thermal shock to the heat exchanger.
 
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Old 09-23-08, 08:25 PM
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You'll only have to worry about the thermal shock in the event that for some reason you pump a lot of cold makeup water into a hot boiler. Under normal operation, this should never happen.

If you are making piping changes though, by all means yes, move the feedwater to the air sep / ET location.
 
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Old 09-24-08, 04:44 AM
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Agree with Trooper. If you are already making piping changes, a much better place for the auto fill is where the expansion tank connects to the system. Often below the air eliminator.

A good generic diagram of the arrangement is at

http://spirotherm.com/docs/installation/JrIOM-A.pdf

(Ignore the 'spirotop' -- that's 99% marketing.)

Add a ball valve just above the tank -- but below the fill assembly -- to facilitate future changes and service.
 
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Old 09-24-08, 05:49 AM
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The main reason for the wet rotor circulator to be mounted on the supply pumping away from the ET is adding pressure to the system. This helps eliminate air from the system. The high point in the system must always be above 4 psi when the pump is running. The change came about with the introduction of wet rotor circulators. They have steeper pump curves that made the difference. With the old 3 piece circulators the pump curves were relatively flat and it did not make much of a difference. It does with wet rotor pumps.
For another siple drawing see this web page.
http://www.comfort-calc.net/pictures...old_Piping.JPG
 
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Old 09-24-08, 06:55 AM
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Thanks rbeck, NJ, and xiphias (swordfish!). You guys have all been a great help. I'll re-plumb the system this weekend to put the ET and the air separator before the circulator in a push away arrangement.

Just as an aside here's some info about what I did in preparation. The original boiler from 1970 was 148 kbtu input and about 118k output. Since the original boiler was installed I have added a 400 sq ft room exposed on three sides, double paned high efficiency windows, and extra attic and wall insulation (I re-sided the house and added 1/2" sheet insulation and Tyvek to the sidewall.)
When I did a heat loss calculation I found that 118K was way too high even with the room addition. I redid the calc. and got the same thing. I couldn't believe that the boiler had been so over capacity so I asked a friend who has a HVAC biz to check my figures. He said I was right and needed a smaller boiler and that's how I ended up with a 104k output boiler.

Just out of curiousity is there some rule of thumb about how long a boiler should run when heating? Mine takes ablout 20 minutes to get up to 230F when it shuts down and then circulates residual heat until needing the flame on again. This is with an exterior temperature about 65F, and an interior temp of 70F, and me setting the t'stat at 74F. This was all done for test purposes. Normally the heating system is not used at all until the outside temp stays below 60, and I set the t'stat to 70.
 

Last edited by rolyf; 09-24-08 at 08:42 AM.
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Old 09-24-08, 08:43 AM
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230F? Not safe. Parts of the system could flash to steam. Turn it down. Should be 180F.

How long a boiler runs depends on a host of things: how cold outside, what kind of heat emitters, what the room temp is, what size it is, how piped, characteristics of system, etc. etc. etc.

Generally the shortest on-cycle should not be less than 5-7 minutes. Very crude rule of thumb based on how long a typical boiler might take to come to steady-state flame, heat the flue passages, etc.
 
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Old 09-24-08, 09:00 AM
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230F? Not safe. Parts of the system could flash to steam. Turn it down. Should be 180F.
Based on everything I've read which you guys reffered me to there is a possibility that my circulator is cavitating and therefore not moving the volume it should. I'll do the repairs I previously mentioned and then re-test. If the temp goes over 180 I'll adjust the shut off point..
 
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Old 09-24-08, 09:21 AM
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If it's cavitating, you'll hear it for sure.

A more telling sign of air problems is "whooshing" and gurgling sounds in the piping and heat emitters throughout the house. Especially upstairs.
 
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Old 09-24-08, 03:44 PM
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Roly, what is the temp wheel on the aquastat currently set at ?

If you are getting 230 water with the aquastat set at 180 I would suggest looking into why such a big difference. It may be that the sensing bulb is not properly inserted and seated into the immersion well...

Make sure when you mount the pump that it's installed according to the recommended and allowed orientation of the motor.
 
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Old 09-24-08, 03:51 PM
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What type of radiation do you have in the home. That time seems exxcessive at 65f and 230f water temp. Asa stated above 230 is way too high. Do not exceed 210 but 180 is better.
 
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Old 09-24-08, 04:53 PM
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Originally Posted by NJ Trooper View Post
Roly, what is the temp wheel on the aquastat currently set at ?

If you are getting 230 water with the aquastat set at 180 I would suggest looking into why such a big difference. It may be that the sensing bulb is not properly inserted and seated into the immersion well...

Make sure when you mount the pump that it's installed according to the recommended and allowed orientation of the motor.
Curiousity got the best of me, I had to know. It's a Honeywell control with a semicircular wheel having the temp's 180 to 220 engraved on it. In front of the wheel is a triangular pointer which I take to be the set point. It was pointed at 220! I thought these units were all set up and ready to go. Obviously this was set at too high a point for my application. I adjusted the wheel to 180 and will see what happens when I test it again later.
I, too, thought 230 was excessive. In case of a rupture or leak the suddenly unpressurized water would flash to steam. Not good.

I have the instruction sheet for the circulator (Taco) and will be installing it correctly which it is except that it is before the ET.
 
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Old 09-24-08, 04:56 PM
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Originally Posted by rbeck View Post
What type of radiation do you have in the home. That time seems exxcessive at 65f and 230f water temp. Asa stated above 230 is way too high. Do not exceed 210 but 180 is better.
I have about 110 feet of baseboard radiators.
 
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Old 09-24-08, 06:36 PM
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Are the baseboards cast iron or copper with aluminum fins ?
 
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Old 09-25-08, 05:41 AM
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Originally Posted by NJ Trooper View Post
Are the baseboards cast iron or copper with aluminum fins ?

Copper with aluminum fins. Oh, and it's 117 ft. by actual measurement.
Since turning the aquastat down the boiler temp. rises to about 190 when running, and when the boiler shuts off it briefly rises to maybe 210 due to heat soak. I'm still wondering why it left the factory set at 220.
I found that the setting dial actually has lower readings, down to 140, but I couldn't see them until I rotated the dial to 180.
 
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Old 09-25-08, 02:58 PM
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I don't think it's a safe bet to assume that ANY boiler comes from the factory set up and ready to 'plug and play' ...

Has any combustion testing been done on the unit ? i.e. CO2, CO, etc ? This should ALWAYS be done on a newly installed system, and preferably yearly during system maintenance. You will be hard pressed to find techs that actually will do it... I don't know why ... even on oil fired systems, it's a chore to get the guys to break out the testing equipment ... seems all they wanna do is change the filter and nozzle, set the electrodes, peer at the flame and mutter: "arrrgggghhhh, that's a SHARP flame!" ...

But, I digress.

Is the 117' all in one single loop ? or are there multiple loops ?

If you have 117' of baseboard in one loop, you will probably see something in the order of a 40 drop from the supply side to the return side. What this would mean is that you will have much less heat output from the baseboards at the end of the loop, perhaps cooler rooms as a result.

If they are multiple loops, how long is the longest one ?

Did you say earlier if the system is zoned or not ?
 
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Old 09-26-08, 01:05 AM
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Originally Posted by NJ Trooper View Post
I don't think it's a safe bet to assume that ANY boiler comes from the factory set up and ready to 'plug and play' ...

Has any combustion testing been done on the unit ? ...
Good morning NJ. The system is single zone, double loop. One loop is about 65', the other 52'. I keep the house comfortable by adjusting the louvers on the baseboards. Generally one adjustment is good for the season (depending on how the room is used, my house only has two of us living in it now). This weekend I will check the return temperatures just for the fun of it.
I have had two oil furnaces and one gas boiler annually checked/maintained/cleaned for almost forty years. Not once was a combustion test suggested or done by the technician. I know this because it was not on the very itemized bills which I received. I don't mention this to argue your point, I agree with you. It just supports the comment you made: "arrrgggghhhh, that's a SHARP flame!" ...
 

Last edited by NJT; 09-26-08 at 05:00 AM.
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Old 09-26-08, 04:59 AM
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Mornin! 4:05AM ? yeah, that's mornin' all right!

Lengths of those loops is perfect... your delta should be be right on the money, probably very close to 20F. That delta T isn't a _critical_ number, as long as the return water is hot enough after a few minutes to avoid flue gas condensation, and the rooms at the end of the loops have enough heat.

135F is generally accepted as a 'safe' temp for return water on a gas boiler.

What this means is that your supply temp would probably be safe to run as low as say 160F during the 'shoulder seasons' (fall and spring) when the home doesn't need as much heat. In other words, the heat loss of the home can be met with lower temp water in the system when the outdoor temps are moderate.

This is the whole idea behind 'OutDoor Reset' (ODR). The ODR control monitors the temp outdoors and adjusts the boiler temp according to a 'heating curve'. With a standard boiler such as yours, the bottom end is limited by the fact that you need at least the minimum return temps stated above. This minimum should be met within say 5 minutes or so, and run at that temp at least a minute or so on each burner cycle. The BOIL MIN setting on the control adjusts for this. Condensing boilers can go all the way down to room temperature because they are designed for this operation.

Is there a 'boiler bypass' installed on your system ?

In the interest of savings, you might consider adding a Tekmar 260 to do ODR for you...
 
 

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